1. Field of the Invention
This invention relates to a disk washing apparatus for washing circular substrate disks of memory media to be used as magnetic disks, optical disks or the like.
2. Prior Art
For example, in the production of magnetic disks which have a magnetic recording film layer formed on the surfaces on the opposite sides of a circular metal substrate of aluminum or the like, the opposite surfaces of the substrate disk need to be washed clean prior to forming the magnetic recording film layers. Not only dusts including polishing powder remaining on the substrate surfaces but also stains of oil films have to be cleaned off by disk washing to put the surfaces in a completely clean state since a trace of dust or blemish could be a trouble to the formation of a recording film. Especially in view of the recent trend toward the adoption thinner recording films for the improvement of recording density or for enhancing the write-in and read-out speeds, a trace of foreign matter or blemish on the surfaces which support a thin recording film will impose great influences on the accuracy of information write-in and read-out operations. Accordingly, washing substrate disks into a completely clean state is a matter of utmost importance from the standpoint of maintaining and improving the quality of magnetic disks.
In this connection, the current disk washing apparatus are largely classified into an ultrasonic wave washing type and a brush washing type. The ultrasonic wave washing type which is extremely effective for removing foreign matter has a problem that it is incapable of removing stains like oil films which have deposited on disk surfaces. On the other hand, the brush washing type which uses a detergent is effective for cleaning off not only foreign matter but also deposited stains from disk surfaces, and for this reason generally accepted these days.
The brush type washing operation generally consists of three stages, more specifically, a washing stage, a rinsing stage and a drying stage. In the washing stage, while supplying a detergent like a neutral cleaning solution, the front and rear surfaces of a disk substrate are brushed to wash off deposited foreign matter and stains from the disk surfaces. In the succeeding rinsing stage, the detergent is washed off with the use of pure water and by either shower rinsing or brush rinsing. Of these two types of rinsing, the brush rinsing is advantageous in a case where perfection is sought for. The last drying stage serves to remove water drops and moisture from the disk surfaces, for example, by the so-called high-speed spin drying in which the disk is put in high speed rotation.
In order to make the disk washing and rinsing more perfect, it is necessary to wash and rinse not only the front and rear disk faces but also the edge portions at the inner and outer peripheries of a disk. For this purpose, it has been the general practice to employ two-step washing and rinsing operations, namely, a washing operation consisting of a first step of brush-washing the edge portions at the outer and/or inner periphery of a disk and a second step of washing the front and rear disk faces, followed by a two-step rinsing operation which similarly consists of a first edge rinsing step and a second face rinsing step.
However, despite the advantage that the entire areas of the disk surfaces are perfectly washed, the two-step washing and rinsing operations have problems that the washing operation involves an increased number of steps and takes a longer time, coupled with a drawback that there has to be provided a washing apparatus of complicate construction and larger size. Besides, there are possibilities of foreign matter or contaminants migrating into and re-spoiling the inner and outer peripheral portions during the face washing subsequent to the edge washing, or possibilities of a detergent re-depositing on the inner and outer peripheral portions during the face rinsing.